From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751451AbdKYJct (ORCPT <rfc822;w@1wt.eu>);
        Sat, 25 Nov 2017 04:32:49 -0500
Received: from mail-wr0-f179.google.com ([209.85.128.179]:39091 "EHLO
        mail-wr0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751326AbdKYJcq (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 25 Nov 2017 04:32:46 -0500
X-Google-Smtp-Source: AGs4zMaPrEBse+L32n6C3MmJdgITKqdArmjVvvCVqrUjgOvz2SrmLSGfwyvZQ4gZi/7OYp4fbV/fTg==
Date: Sat, 25 Nov 2017 10:32:43 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [crash] PANIC: double fault, error_code: 0x0
Message-ID: <20171125093243.4gmkelmyb4mnhvos@gmail.com>
References: <20171124172411.19476-1-mingo@kernel.org>
 <20171124202237.oytdkqq25s3ak2ul@gmail.com>
 <20171124220934.q7ovq4yzaihevqls@gmail.com>
 <464B14E7-EC38-4A5A-8BF6-B086F437C6D1@amacapital.net>
 <20171124225311.zpbgsejobpzxm7tb@gmail.com>
 <20171125092113.p2shs3hjy6q2mip2@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20171125092113.p2shs3hjy6q2mip2@gmail.com>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Ingo Molnar <mingo@kernel.org> wrote:

> > (Also note that in my config NR_CPUS is at 128 - defconfigs are 64.)
> 
> The simplest padding I found is the one below - this indicates some sort of 
> section sizing or page table setup bug (or page alignment bug) and makes races and 
> other bugs less likely.
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 4ac952080869..ea992ca4e74f 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -547,6 +547,8 @@ END(irq_entries_start)
>  	ud2
>  .Lokay_\@:
>  	addq $8, %rsp
> +#else
> +	.rep 64; nop; .endr

Also note that turning off CONFIG_UNWINDER_ORC also solves the crash. I did that 
in an attempt to get a different backtrace.

So it's either unwinder related, or seemingly minor changes to code 
alignment/placement will make the bug go away.

Thanks,

	Ingo